Subscribers and network operators increasingly require faster and more comprehensive access to existing and new services. This is where the concept of the intelligent network `IN` is applied. The basic idea is the introduction of a new control level, which centrally contains the service data and logic, and controls development of the services in a telecommunications net-work.
The standards for such a telecommunications network of the Pan-European digital cellular mobile transmission system GSM (i.e. Group Special Mobile of the CEPT (Conference Europeenne des administrations des Postes et Telecommunications)) were established at the European conference of Mail and Telecommunication Administrations.
To establish a connection for mobile subscribers of this network, after the receiver is lifted or an entitlement card is inserted into a terminal, an identification signal is transmitted to the mobile transmission relay MSC (i.e. GSM Mobile-service Switching Centre), which performs an intelligent network function. The mobile transmission relay requests a so-called visiting location register=VLR and/or a home location register=HLR, and uses these data to establish a connection ("Intelligent Networks--Performance Basis for Future Services", B. Eske--Christensen, K. Schreier, D. Stroh, telecon report 12(1989) Book 4, pages 102-105).